There is an increasing need for long term observation of the earth-ocean system. In particular, there is a need to study, identify and quantify the chemical constituents present in the water column including dissolved gases such as methane, hydrogen sulfide, nitrogen, carbon dioxide and oxygen. A study of the chemical constituents enables scientists to track changes in theses chemicals over time and thereby monitor oceanic processes as well as improve predictive modeling of complex natural phenomena that vary over a longer time-scale. In general, such a study has a wide range of scientific, industrial, environmental and military uses including monitoring shipping lanes, and monitoring and mitigating hazardous chemicals.
Cabled observatories located near the ocean bed allow for continuous in-situ sampling of the underwater environments at desired sites. Since they are typically located in a particular site and tethered to the ocean floor, they have several advantages including having ability to capture significant transient phenomena and sudden changes in the ocean environment, and since they are in-situ, eliminating the problems associated with sample transportation and storage. However, current technologies for studying the chemical constituents using these cabled observatories for reliable long-term operation underwater are limited. These cabled observatories are typically equipped with commercially available dissolved gas sensors, such as the Clark type oxygen electrode, that are capable of measuring only single gas species and operate for only a few weeks before degrading in performance. More powerful instrumentation such as gas chromatographs are not suited for autonomous long-term underwater operation since they need consumables and require regular maintenance. An increasing trend is the use of mass spectrometers in cabled observatories.
Mass spectrometers are well suited for in-situ analysis of dissolved gases and volatile chemicals in the water column, because they can quickly detect multiple dissolved chemicals at low concentrations, and can work without exhaust or consumable reagents. However, current autonomous platforms such as moorings, tow fish and autonomous underwater vehicles utilizing mass spectrometers preclude long-term seafloor use because they do not have the endurance or depth capability. Additionally, they are unable to adequately resolve low mass chemicals such as hydrogen, helium and methane. Such systems are described in the MIT PhD thesis titled “Creation and Deployment of the NEREUS Autonomous Underwater Chemical Analyzer and Kemonaut, an Odyssey Class Submarine” dated May 2003 and MIT Masters thesis titled “The Development of Components for In-Situ Mass Spectrometer” dated May 2000, the contents of each of which are incorporated herein by reference in their entirety.
Accordingly, there is a need for a submersible system to perform long-term series sampling of dissolved gases in a water column in the ocean depths (e.g., at depths greater than 2500 m). There is also a need for a reduced size mass spectrometer devices that can facilitate, among other things, mobile sensing devices that may move through the ocean environment and take samples over a large geographic area.
In addition to analyzing underwater environments, there is a need for accurate observation of atmospheric and subsurface environments. In particular, there is a need for a fast and reliable system for detecting hazardous gases in populated urban centers where the speed and accuracy of detection can save lives in the event of chemical spills or acts of bio-terrorism. Similarly, in oil and natural gas applications, there is a need for measuring volatile gases such as hydrocarbons while controlling the seepage of water vapor into the instrumentation. Current systems typically utilize infra-red sensors that are prone to error from unwanted atmospheric water vapor molecules entering the measurement system. Furthermore, current systems do not utilize more sensitive mass spectrometers because they require the continuous maintenance of low pressure conditions and strict control of substances entering the instrumentation.
Accordingly, there is a need for compact systems capable of being operated with mass spectrometers to analyze oceanic, atmospheric and subsurface environments. Generally, there is a need for a compact system to sample and detect volatile substances and dissolved gases in both underwater as well as atmospheric environments both over and under the surface of the earth.